Plate for osteosynthesis device and method of preassembling such device

ABSTRACT

Various methods, devices, and systems are disclosed that facilitate easier and more compact implantation of osteosynthesis devices. In some embodiments, implants are screwed into two vertebrae and a plate is used to hold and displace the spine. In some plate embodiments, at least one longitudinally elongated opening is disposed at one end of the plate and partially opening onto an edge of the plate. In some plate embodiments, at least one longitudinally elongated opening is disposed at one end of the plate having a portion sufficiently large to be inserted without disassembly in the fixation means of an implant already screwed into the spine when the fixation means are already assembled.

This application is a continuation of U.S. patent application Ser. No.10/492,827, filed Jul. 15, 2004, and issuing Apr. 24, 2012, as U.S. Pat.No. 8,162,988, which is a National Stage entry of InternationalApplication No. PCT/IB02/04307, filed Oct. 18, 2002, which claimspriority to French Patent Application No. 01/13460, filed Oct. 18, 2001,all of which are incorporated herein by reference.

The present invention relates to an osteosynthesis device, particularlyfor spinal support or correction, enabling easier and compactimplantation, that can be particularly used in the case of implantationvia the anterior approach, and a preassembly method for such a device.

For spinal support or correction, a device comprising one or moresupport bars or plates positioned along the spinal column is used, andfixed to certain vertebrae by implants. Said implants are fixed at oneend to the plate and at the other end to the vertebrae by bone anchoragemeans, for example a threaded part screwed inside the actual vertebra.

In such devices, it is known to use a plate comprising several holes, tojoin the implants fixed to several vertebrae, as described in the patentFR2726171, for example. Said bars then surround or pass through the headof the screw and are locked with a nut screwed onto said head.

However, such a device requires that the clamping nut only be fitted onthe screw after the screws and the plate have been positioned.Therefore, said nut can only be inserted onto the screw head during theoperation, with all the difficulties and risks of loss that may becaused by handling and assembling a small part inside a human body. Thisoperation is all the more problematic when said operation is conductedby means of endoscopy, for example when it is necessary to implant viathe anterior approach, i.e. via the front of the body or on the frontface of the spine.

A device according to the prior art also requires that the implants befixed and completely clamped before the plate is positioned. Therefore,in the event of delicate operative conditions, it is difficult tosuccessfully position the plate very close to the spine. This problemarises for example when the shape of the spine comprises too manyirregularities, due to spinal displacement or deformation or in thepresence of outgrowths such as osteophytes. There are similar problemsin the case of implantation by the anterior approach, i.e. via the frontof the body or on the front face of the spine. Indeed, the anatomicalconditions in this case frequently only leave space for a compact size.In addition, it is often necessary to work by means of endoscopy in thiscase, which renders the operation difficult and gives a lesssatisfactory view of the implant insertion depth.

In some cases, to enable subsequent consolidation of the fixationbetween the implant and the vertebra, an implant composed of a so-called“rehabitable” screw is used, i.e. a hollow screw wherein the insidecommunicates with the outside via openings passing through the threadedwall. During the screwing into the vertebra, part of the bone substancepenetrates inside the screw. Over time, the bone substance fuses betweenthe inside and outside of the screw via these openings, thus formingconsolidation over time.

In this way, the patent FR 2726171 discloses a hollow screw wherein theopenings are produced by cutting on the inner surfaces of said screwlongitudinal grooves which cut into the base of the outer threading.However, during positioning or subsequently, such a screw may formanchoring which is not sufficiently strong and is liable to be dislodgedor torn from the vertebra wherein it is implanted.

One of the aims of the invention of the invention is to propose a platethat can be fitted on preassembled implants already screwed into thespine.

Another aim of the invention is to propose an osteosynthesis device thatcan be partly preassembled before the operation to enable easierimplantation.

In this way, the invention relates to a device as described above,characterised in that the plate has an elongated shape and comprises onat least one of its ends at least one longitudinally elongated opening,said opening having firstly at least one part opening onto an edge ofthe plate, or one part of a sufficiently large size to be able to beinserted without disassembly in the fixation means of an implant alreadyscrewed into the spine when said fixation means are already assembled,and secondly one part of a roughly constant width and able to slidelongitudinally in the fixation means of said implant after having beeninserted and of being fixed thereon; such a plate can thus be assembledby one end to an already fitted implant, and then slide in the fixationmeans of said implant to insert the other end in another already fittedimplant, and then slide again to bring both ends into the fixationposition, while the fixation means of said two implants were assembledbefore being fitting onto the spine.

According to one embodiment, the plate comprises two parts of identicallengths or not, said two parts being joined together by a joining part,said joining part being located in an inner part of the plate, i.e. at asufficient distance from the ends to enable the fixation of the plateonto two implants, at a rate of one implant on either side of saidjoining part.

According to one embodiment, the joining part is located in a positionoffset with respect to the centre of the plate length.

According to one embodiment, the plate has an “H” or “h” shape.

According to one embodiment, the plate has at least one longitudinallyelongated opening, wherein a first region is of constant width and asecond region is larger in size than the first region, said openingbeing able to allow the fixation means of an implant to pass beforesliding to bring said fixation means in the first region.

Another aim of the invention is to propose a compact osteosynthesisdevice, that can be fitted and adjusted in a position very close to thespine.

This aim is achieved by an osteosynthesis device, particularly for thespine, comprising a plurality of implants that can be screwed into oneor more vertebrae and provide a rigid joint between said vertebrae andat least one plate or bar used to hold or displace the spine,characterised in that the plate is joined to at least one implant byfixation means able to hold said plate without preventing the implantfrom rotating on its screwing axis, or without preventing a specifiedclearance of the plate with respect to the implant, or both: thus makingit possible to continue screwing the implant, or adjust the position ofthe plate, or both, after the plate has been assembled on the implant.

According to one embodiment, at least one implant has an elongated shapearound an axis, referred to as the implant axis, and comprises a firstbone anchoring end bearing at least one threading and a second end withan elongated part passing through a plate support, said plate supportbeing free in rotation around said elongated part, said elongated partbearing clamping means able to hold and clamp the plate against saidplate support.

Another aim of the invention is to propose an osteosynthesis device thatcan be screwed or clamped when it is not possible to use a tool in theactual axis of the implant.

This aim is achieved by a device as described above, characterised inthat the elongated part, referred to as the clamping support, of theimplant is mobile with respect to the rest of the implant, along auniversal type joint between a part of the implant referred to as thescrew head and a part of the clamping support referred to as the supporthead, thus making it possible to continue screwing the implant after theplate has been assembled on the implant, by rotating the clampingsupport around a clamping support axis, when said axis forms a non-nullangle with the axis of the implant.

According to one embodiment, the plate surrounds the clamping support orthe second end of the implant at least partly and rests on a surface ofits complementary plate support, said plate support having on theimplant side a concave surface in the form of a spherical portion whichis supported in a complementary fashion on the outer surface of theimplant screw head.

According to one embodiment, the clamping support has a first elongatedend along the support axis and a second end bearing the support head,said support head having a non-circular cross-section having at leastone concave part and comprising at least one dimension greater than atleast one cross-section of the first end of the clamping support; saidsupport head having firstly one section roughly partly circular along aplane including the support axis, and being secondly arranged in thescrew head inside a housing wherein the inner surface has at least oneprojecting part cooperating with the concave part of the support head toprevent rotation of the clamping support around its axis.

According to one embodiment, the inner surface of the screw head housinghas a shape roughly complementary to the outer surface of the supporthead.

According to one embodiment, the housing receiving the support head has,on the side of said clamping head, a specified dimension to allow theclamping support a clearance along a specified angle, between the axisof the clamping support and the axis of the implant, without saidclamping support escaping from said housing.

According to one embodiment, the clamping support head has a star-shapedcross-section with rounded ends, along a plane perpendicular to thesupport axis.

According to one embodiment, the clamping support clamping meanscomprise a threading cooperating with a nut to hold or clamp the plateagainst the plate support.

According to one embodiment, the clamping support comprises at its endopposite the implant an inner or outer recess capable of receiving arotational drive tool and thus enable the screwing or clamping of theimplant in the vertebra.

One of the aims of the invention is to propose an osteosynthesis deviceenabling improved screw implantation strength, during fitting, duringthe period prior to bone fusion or after consolidation.

This aim is achieved by a device such as that described above,characterised in that the first bone anchorage end of at least oneimplant has a longitudinal bore concentric to its outer surface, saidbore communicating with the outside by at least one bone fusion openingproduced in the wall between said inner bore and said outer surface,thus enabling a fusion between the inside and the outside of the bonesubstance in contact with said first end.

According to one embodiment, the first bone anchorage end of at leastone implant has two threadings winding in the same direction during thescrewing of the implant, and borne respectively by the outer surface ofsaid first end and the inner surface of the bore that it comprises.

According to one embodiment, at least one bone fusion opening has theshape of a longitudinal oblong hole.

Another aim of the invention is to propose a preassembly method for suchan osteosynthesis device.

This aim is achieved by the preassembly method for a device according tothe invention, characterised in that it comprises the following steps:

-   -   assembly of the plate support on the clamping support of an        implant;    -   assembly of the nut on the threading of the clamping support of        said implant.

The invention, with its characteristics and advantages, will be seenmore clearly upon reading the description with reference to the appendedfigures wherein:

FIGS. 1 a, 1 b, and 1 c represent an osteosynthesis device according tothe invention in an embodiment comprising an “H”-shaped plate and twopolyaxial head implants fitted on an interval vertebra, in threesuccessive phases of the fitting of the plate in the implants;

FIG. 2 represents a longitudinal section view of an implant of a deviceaccording to the invention in the implant clamping phase after insertionof the plate, in an embodiment comprising a plate support free to rotatearound a rehabitable hollow screw implant and fixed clamping support;

FIG. 3 represents a longitudinal section view of an implant of a deviceaccording to the invention in the implant clamping phase after insertionof the plate, in an embodiment comprising a plate support free to rotatearound a rehabitable hollow screw implant and inclinable clampingsupport;

FIG. 3 a represents a partial view of an implant according to theinvention, in a section along a plane passing through the centre of thesupport head and perpendicular to the support axis;

FIG. 4 represents a longitudinal section view of an implant of a deviceaccording to the invention in the plate clamping phase once the implantis in its definitive position, in an embodiment comprising a platesupport free to rotate around a rehabitable hollow screw implant andinclinable clamping support;

FIGS. 5 a, 5 b, 5 c and 5 d represent a top view of a plate of a deviceaccording to the invention, in an embodiment comprising a plate which isrespectively “H”-shaped with two through openings, “h”-shaped with onethrough opening, with two non-through openings and with one non-throughopening;

FIG. 6 represents a side view of an implant of the preassembled deviceaccording to the invention, in an embodiment comprising an inclinableclamping support and a rehabitable hollow screw with two oblong holes;

FIG. 7 a represents a perspective view of a longitudinal section of animplant of a device according to the invention, in an embodimentcomprising an inclinable clamping support and a rehabitable hollow screwwith two oblong holes and according to an alternative embodiment wherethe screw head housing and the support head interact without beingcomplementary in shape;

FIG. 7 b represents a partial perspective view of the support head of animplant of a device according to the invention in the same alternativeembodiment;

FIG. 7 c represents a partial perspective view of a cross-section alongthe plane AA of an implant of a device according to the invention in thesame alternative embodiment;

FIG. 8 represents an osteosynthesis device according to the invention inan embodiment comprising an “H”-shaped plate and two polyaxial headimplants according to an alternative embodiment where the implants onlycomprise a single threaded part, on their outer surface.

In an embodiment represented in FIG. 2, the device according to theinvention comprises an implant 1 comprising a first end 11 equipped withan outer threading 111, and is illustrated after a first screwing in thebone substance of a vertebra 0, after insertion of a plate 2 and duringthe final approach. Said first end 11 also comprises a cavity or aninner bore, itself equipped with an inner threading 112 wherein thescrewing direction is the same as that of the outer threading 111.During the screwing of the implant into the vertebra 0, part of the bonesubstance tends to fill said cavity and is assisted therein by theaction of the inner threading. Preferentially, the inner threading 112and the outer threading 111 are of the same pitch, so as to minimise thestrain exerted on the bone substance at the entry of the bore duringscrewing.

The wall between the inner cavity and the outside of the implant has oneor more openings, referred to as bone fusion holes 110, in its partwhich is inside the vertebra after the clamping of the implant. In theperiods following the implantation, generally approximately six months,the bone substance present outside and inside the implant tends to fuse.The fusing produced in this way improves the strength of saidimplantation, both by means of blocking via the bone fusion holes 110,and by means of cooperation of the inner threading 112 with the bone pinformed in this way.

In one alternative embodiment, the inner threading 112 has a greaterpitch than that of the outer threading 111. During the screwing of theimplant 1, the bone substance present inside the cavity is thenattracted slightly more quickly than the implant progresses in thevertebra 0. This effect may make it possible to compensate for a fillingdefect liable to occur, for example by compression of the bone substanceinside the bore. This effect may also make it possible to obtain morecomplete or more compact filling of said cavity, for example in order toobtain a specific compression or better filling of the cavity or thebone fusion holes 110, and thus favour bone substance fusion.

At its second end, i.e. opposite the vertebra, the implant 1 comprisesfixation means used to insert, hold and finally clamp a bar or a plate2. Said second end also comprises drive means using a tool of knowntype, such as a hexagonal recess 124.

Said fixation means comprise for example an elongated part 12 a of across-section less than the central part of the implant, comprising ashoulder. Said elongated part 12 a passes through a plate support 3resting on said shoulder, and comprises at its end a threading 123receiving a clamping nut 4. In one embodiment, said plate 2, FIG. 5 a,is roughly “H”-shaped, comprising for example two cylindrical barsjoined at their centre by a rigid distance sleeve. In an alternativeembodiment, the two bars are joined by a non-rigid joint enabling morelatitude in the positioning of the plate. Said plate 2 is insertedbetween the plate support 3 and the nut 4, so as to surround theelongated part 12 a of the implant. Once the plate is in position, thenut 4 is fastened, by hand or using a tool of a known type 52, FIG. 4,and cooperates with the threading 123 to clamp the plate 2 against theplate support 3 and thus lock the fixation.

In said embodiment, the plate support 3 comprises a bore 30 with aroughly rectangular insert passing through its centre. Said platesupport 3, on the side of the plate, has one or more roughlycomplementary surfaces 2 to the surface of the plate 2 resting on them.In said embodiment, the central bore of the plate support 3 issufficiently larger than the part 12 a passing through it to allow aclearance of said support 3 transversally and at an angle with respectto the axis d1 of the implant. Said clearance makes it possible toadjust the relative position of the plate supports of two implants 1, 1a easily, and thus insert the plate 2 easily even if the implants arenot well aligned or in the event of a relatively inaccessible anatomicalenvironment. According to an alternative embodiment not shown, the platesupport receives a plate 2 a, FIG. 5 b, comprising a single bar at oneof its ends. Said plate support can then comprise an offset bore insteadof the central bore 30, without leaving the scope of the invention.

Since the plate support 3 is free in rotation around the part 12 a ofthe implant 1, it is clearly understood that it is possible to continuescrewing said implant into the vertebra 0, even when the plate isalready in position, provided that the fixation means are not fastenedon said plate 2. In this way, by inserting the plate 2 into saidfixation means before the implant 1 is not entirely screwed on, it ispossible not to be hindered by the various differences in levels oroutgrowths liable to be present in the immediate vicinity of the spine.Once the plate is held in place but not clamped, it is still possible tofinish screwing the implant into the vertebra, by rotating it via anopening of the plate support 3. The fixation means then hold the plate 2close to the spine, the screwing of the implant providing sufficientforce to oblige the plate to come closer to the spine. Therefore, theplate can be positioned and inserted with little effort, while beingpositioned definitively very close to the surface of the vertebra, whichmakes it possible to obtain a compact device size once fitted.

In a preferential embodiment of the device according to the invention,represented in FIGS. 3, 3 a and 4, the implant 1 comprises a mobilepart, referred to as the clamping support 12, at its second end oppositethe first end 11 screwing into the vertebra 0. Said clamping support 12has an elongated first end 121 along a support axis d12. Said elongatedend passes through the central bore of the plate support 3 and bears athreading 123 receiving the clamping nut 4.

At a second end opposite its elongated end 121, the clamping support 12bears a part, referred to as the support head 122, joining said clampingsupport 12 to the implant by its second end, referred to as the screwhead 102, opposite the end 11 screwed into the vertebra 0. Along a planeperpendicular to the support axis d12, said clamping support head 122has at least one dimension s122; FIG. 3 a, greater than at least onecross-section s121 of the elongated end 121 of said clamping support 12.Said support head 122 is retained in a housing provided in the screwhead 102 of the implant 1. For this purpose, said housing has an openingof a specified size s102 so as to retain the support head 122 insidesaid housing, while allowing a clearance of a specified angle a betweenthe support axis d12 and the implant axis d1.

Said angular clearance of the clamping support 12 with respect to theimplant enables angular and lateral movements facilitating to theinsertion of the plate in the fixation means of the implant, asdescribed below. Said angular clearance also makes it possible tocompensate for any alignment defects between the different implants 1, 1a; FIG. 1 c, of a device according to the invention and thereforerenders the positioning of the plate 2 in the fixation means of saidimplants less delicate.

In said preferential embodiment, the plate support 3 rests on the screwhead 102 of the implant 1, by means of a lower surface 31 composing aspherical portion for example. Said lower surface 31 of the platesupport is in complementary contact with an upper surface 13 of saidscrew head. Said spherical complementary contact allows freedom ofrotation and inclination of the plate support 3 with respect to theimplant 1. Said spherical complementary contact of said surfaces 13, 31also enables a uniform and stable support of said surfaces with respectto each other, after the plate 2 has been clamped onto the platesupport, irrespective of the definitive angular position of said platesupport 3 or the clamping support 12.

The implant 1 is screwed into the vertebra 0 by means of a rotationaldrive of said implant by rotating the clamping support 12 around its ownclamping axis d12. Said clamping support is rotated for example by atool, of known type, inserted into at least one recess 124 contained inthe elongated end 121 of said clamping support. The clamping support 12rotates the implant 1 by means of a universal type joint, i.e. therotation of either of the two components around its axis rotates theother component around its own axis, the angle between the two axespossibly being non-null.

Said universal joint is produced by the cooperation of the outer surface120 of the support head 122 with the inner surface 100 of the housing ofthe screw head 102 of the implant 1. Along a plane perpendicular to thesupport axis d12, the support head 12 has a section with a non-circularoutline, for example in the shape of a star or cross with roundedcorners, as illustrated in FIG. 3 a. The housing of the screw head 102which receives the support head 122, then has an inner surface 100 inroughly complementary contact with the outer surface 120 of said supporthead 122, said two surfaces 100, 120 cooperating to form the rotationaljoin between these two components 102, 122. The angular variation isallowed by the fact that the support head 122, and its complementaryhousing, have a section with a circular outline along at least one planeincluding the clamping support axis d12, or the implant axis d1, orboth.

According to an alternative embodiment illustrated in FIGS. 7 a to 7 c,the inner surface 100 of the screw head housing receiving the supporthead simply has one or more projecting parts 100 a, for example two. Theouter surface 120 of the support head 122 then has one or more concaveparts 120 a with which the projecting parts 100 a of the screw headhousing cooperate to prevent the rotation of the clamping support 12around its axis d12.

In this way, it is clear that it is possible to continue screwing theimplant 1 into the vertebra 0, while the plate 2 is already insertedbetween the clamping nut 4 and the plate support 3, by adjusting theelongated end 121 of the clamping support 12 accessible via the nut 4.Since the plate support 3 is free to rotate with respect to the implant1, said implant can rotate during screwing while leaving the plate 2 andthe plate support 3 immobile.

Once the implant 1 is completely screwed into the vertebra 0, asillustrated in FIG. 4, the plate 2 can then be adjusted and locked inits definitive position, by tightening the clamping nut 4. Said nut maybe tightened by hand, for example on a knurled part of its outer surfaceon the support axis d12, or using a tool 52 of known type, for exampleby adjusting two inner or outer recesses on the nut.

According to an alternative embodiment illustrated in FIG. 8, a deviceaccording to the invention uses such implants but wherein the end 11intended to be anchored in the vertebra only comprises one outerthreaded part 111. In said alternative embodiment, the implant maycomprise a longitudinal bore passing through it from one end to another,to enable positioning by means of sliding around a pin implantedbeforehand in the vertebra.

Several implants according to various alternative embodiments in thesame device can of course be combined without leaving the scope of theinvention.

Depending on the applications, in order to join two implants 1, 1 a;FIG. 1 c, it is possible to use a plate of different configurations, forexample such as those represented in FIGS. 5 a, 5 b, 5 c and 5 d.

In the example of an embodiment illustrated in FIGS. 1 a, 1 b, and 1 c,two implants 1, 1 a are screwed into the body of two vertebrae 0, 0 arespectively of the spine, spaced by an interval of one vertebra. Thesetwo implants are then fixed together by a plate 2 inserted into theirfixation means around the clamping support and then clamped between theplate support and the nut of each of said implants.

In the preferential embodiment represented in FIG. 5 a, the plate 2 iselongated in shape and comprises two roughly parallel bars 201, 202,which are for example cylindrical, joined together in a rigid orflexible manner by a joining part 20. Said joining part joins the twobars at an inner part of the plate, i.e. at a specified non-nulldistance from each of the ends 21, 22 of the plate. More specifically,said joining part is located at a sufficient distance from each end ofthe plate so that said end can be inserted into the fixation means of animplant, and possibly slide in said fixation means. The position of saidjoining part 20 may be located at the centre of the plate, or be offsetto allow a greater clearance for sliding during insertion as explainedbelow.

At each end 21, 22 respectively, of the plate 2, the space between thetwo bars forms an opening 210, 220 respectively, opening out onto theedge of the plate. Said openings have a roughly constant transversal gaps211, s221, enabling longitudinal sliding of the plate in the fixationmeans of an implant 1, 1 a. This roughly constant transversal gap alsomakes it possible to clamp said fixation means in any part of saidopenings 210, 220. Since said openings open onto the edge of the plate,it is possible to insert each of the ends of the plate into the fixationmeans of an implant 1, 1 a as illustrated in FIG. 1 a, without having toremove the nut 4 if it was preassembled beforehand. At each end, thisinsertion consists of sliding the end of the two bars between the nut 4and the plate support 3 of the implant 1, at either side of the clampingsupport 12.

In another embodiment represented in FIG. 5 b, the plate 2 a iselongated in shape and comprises a first end 21 a comprising a singlebar, which is cylindrical for example. Said first end can be insertedinto an implant according to the prior art or into an implant asdescribed in the present invention, for example in an alternativeembodiment (not shown) where the plate support only comprises a singlesurface 32 in contact with the plate. The plate 2 a also has a secondend 22 a comprising two roughly parallel bars, which are cylindrical forexample. These two bars form a longitudinally elongated opening 220 atogether, of a roughly constant width s221 a. Either of the two ends ofsaid plate 2 a can be inserted, or slide, or both, in the fixation meansof an implant according to the invention, in the manner described in thepreferential embodiment.

In another embodiment represented in FIG. 5 c, the plate 2 b iselongated in shape and comprises a first end 21 b having at least oneopening 210 b and a second end 22 b having at least one second opening220 b, at least one of these openings not opening onto the edge of theplate 2 b. These two openings 210 b, 220 b have a longitudinallyelongated shape, i.e. along the length of the plate, and may beseparated by one or more joining parts 20. These two openings have aroughly constant width s211 b, s221 b, and can be positioned by means ofsliding and then be clamped in the fixation means of the implants. Atleast one of said openings has a part, referred to as a notch, of alarger size s210 b, s220 b, of a shape and size able to allow the nut 4of the fixation means of an implant to pass through. Therefore, such abar 2 b can also be inserted in the fixation means of an implant 1 whensaid fixation means are already assembled, therefore not requiringhandling, in the patient's body, of small parts such as the nut 4 or theplate support 3.

In an alternative embodiment represented in FIG. 5 d, the plate 2 c hasa single opening comprising two notches as described above (see FIG. 5c). In an embodiment not shown, the plate may comprise a sufficientnumber of openings and notches to be able to assemble the plate withmore than two implants.

It is clear that these different types of openings, which are eitherthrough or have a wider part, can be combined in various ways withoutleaving the scope of the invention.

In the same way, the position of the joining part 20 can vary and beoffset along the length of the plate, so as to leave the clearancerequired for the plate to slide during positioning. In a preferentialembodiment, said position is slightly offset with respect to the centreof the plate, so as to be able to slide the plate sufficiently in thefirst implant 1; FIG. 1 b, to be able to insert it into the secondimplant 1 a.

It is necessary to understand here that the device described can equallywell comprise any other combination of different alternative embodimentsof plates and alternative embodiments of implants without leaving thescope of the invention.

FIGS. 1 a, 1 b, and 1 c illustrate different steps in the positioning ofthe plate 2 in two implants 1, 1 a, in the preferential embodiment. Thispositioning is carried out while the implants are already screwed intothe spine, their fixation means, in this case the plate support 3 andthe nut 4 being already assembled on the implant but not clamped.

In this way, in FIG. 1 a, a first end 21 of the plate 2 is inserted inthe fixation means of the first implant 1, on the plate support 3 andunder the nut 4, straddled around the clamping support 12.

Once this first end 21 has been inserted, due to the fact that the barshave a roughly constant gap, it is possible to slide the plate in thefixation means of the first implant 1 until the second end 22 of theplate can be aligned (FIG. 1 b) in front of the fixation means of thesecond implant 1 a.

By sliding the plate in the opposite direction, it is then possible toinsert (FIG. 1 c) said second end 22 in a similar manner in the fixationmeans of the second implant 1 a. It is them possible to adjust thedefinitive position of the plate 2 and tighten the nut of the fixationmeans of each of the two implants, and thus stiffen the assembly.

In this way, it is clear that it is possible to prepare theosteosynthesis device in advance using the preassembly method,comprising the following steps:

-   -   assembly of the plate support 3 around the clamping support;    -   assembly of the nut 4 on the threading 123 of the clamping        support.

Once it has been preassembled using this method, an implant 1 of thedevice according to the invention can be used directly during thesurgical operation, as represented in FIG. 6.

The osteosynthesis device can then be positioned using the followingsteps:

-   -   the implants are screwed into the spine, without inserting them        to the definitive depth. This approach position makes it        possible not to be hindered by any osteophytes when positioning        the plate 2.    -   The plate 2 is inserted via a first end 21 into a first implant        1. It is then slid into said first implant to be presented in        front of the fixation means of the second implant 1 a. The        second end 22 is then inserted into the second implant. This        positioning is illustrated in FIGS. 1 a, 1 b, and 1 c.

At this stage and subsequently, the clearance of the plate support 3around the clamping support 12 allows the angular and lateral movementsrequired for insertion. This clearance also makes it possible tocompensate for any alignment defects between the two implants 1, 1 a,and thus renders the positioning of the plate 2 less delicate.

-   -   The screwing of the two implants into the spine is then        completed until they are clamped in their definitive position.        This screwing is performed (FIG. 3) using a tool of known type        rotating the implant by means of a rotation of the clamping        support 12. Since the plate 2 is already in position and held in        place by the fixation means of the implants, this additional        screwing of the implants drives the plate to its definitive        position close to the spine. Therefore, this driving obtained by        screwing the implants makes it possible to reduce the size        determined by said plate, by tightening or inlaying said plate        firmly and easily on the surface of the spine.    -   Once the implants have been completely screwed on, the plate is        locked in the fixation means of the implants, by clamping        (FIG. 4) their nut 4 on the plate 2 itself resting on the plate        support 3 which rests on the shoulder or on the screw head 102        of the implant. Naturally, said clamping may be carried out        using other parts not mentioned, such as washers or locking        devices of known types.

It must be clear to those skilled in the art that the present inventionenables other embodiments in numerous other specific forms withoutleaving the scope of the invention as claimed. As a result, the presentembodiments must be considered as illustrations, but may be modified inthe field defined by the scope of the fixed claims, and the inventionmust not be restricted to the details given above.

The invention claimed is:
 1. An implant for securing a spinalstabilization bar to a vertebra, the implant comprising: a bone screwhaving a longitudinal screw axis and comprising a bone penetration enddisposed at a first end of the longitudinal screw axis and a protrusionend disposed at a second end of the longitudinal screw axis distal fromthe bone penetration end; a clamping head having a longitudinal clampinghead axis and comprising a support head disposed at a first end of thelongitudinal clamping head axis, a drive coupler disposed at a secondend of the longitudinal clamping head axis and configured for engagementwith a drive tool to impart rotation to the bone screw, a stabilizationbar support configured to receive a stabilization bar from the side ofthe implant, and a clamp configured to secure the stabilization bar tothe stabilization bar support; and a universal joint coupling the bonescrew and the clamping head.
 2. The implant of claim 1, in which thebone screw further comprises a threaded portion disposed along anexternal surface of the bone screw and configured for screwing into abone.
 3. The implant of claim 1, in which the bone screw furthercomprises a threaded portion disposed along a hollow core that has abone-fusion opening.
 4. The implant of claim 1, in which thestabilization bar support comprises a partially cylindrical surfacecomplementary to a cylindrical surface of a stabilization bar.
 5. Theimplant of claim 1, in which universal joint is configured fortransmission of a rotation of the clamping head around its longitudinalclamping head axis imparted at the drive coupler to a rotation of thebone screw around its longitudinal screw axis while an angle between thelongitudinal clamping head axis and the longitudinal screw axis isnon-zero, and the stabilization bar support is configured to permit saidtransmission while the bar is attached to the implant.
 6. The implant ofclaim 1, in which the drive coupler comprises a hexagonal recess and theclamp comprises a nut.
 7. The implant of claim 1, in which thestabilization bar support comprises an opening configured for rotatabledisposition of the stabilization bar support about the longitudinalclamping head axis.
 8. The implant of claim 1, in which thestabilization bar support and the protrusion end have complementarysurfaces configured for support of the stabilization bar support by theprotrusion end.
 9. The implant of claim 8, in which the complementarysurfaces are partially spherical.
 10. The implant of claim 1, in whichthe protrusion end comprises a housing in which the support head isdisposed, and the protrusion end has a projection configured tocooperate with a concave portion of the support head to preventrotation, relative to the bone screw, of the clamping head around itslongitudinal clamping head axis.
 11. The implant of claim 1, in whichthe stabilization bar support is rotatable around the longitudinalclamping head axis.
 12. An implant for securing a spinal stabilizationbar to a vertebra, the implant comprising: an elongated bone screwhaving a longitudinal screw axis; a clamping head having a longitudinalclamping head axis; a universal joint coupling the bone screw and theclamping head configured for transmission of a rotation of the clampinghead around its longitudinal clamping head axis to a rotation of thebone screw around its longitudinal screw axis while an angle between thelongitudinal clamping head axis and the longitudinal screw axis isnon-zero; a stabilization bar support configured to receive astabilization bar; and a stabilization bar support configured to permitsaid transmission while the bar is attached to the implant.
 13. Theimplant of claim 12, in which the stabilization bar support is rotatablearound the longitudinal clamping head axis.
 14. The implant of claim 13,in which the bone screw further comprises a threaded portion disposedalong a hollow core that has a bone-fusion opening.
 15. The implant ofclaim 14, in which the stabilization bar support comprises a partiallycylindrical surface complementary to a cylindrical surface of astabilization bar.
 16. The implant of claim 15, in which thestabilization bar support and an end of the bone screw havecomplementary surfaces configured for support of the stabilization barsupport by the end of the bone screw.
 17. A system for spinalstabilization comprising: a plurality of implants each comprising: anelongated bone screw having a longitudinal screw axis, a clamping headhaving a longitudinal clamping head axis, a universal joint coupling thebone screw and the clamping head configured for transmission of arotation of the clamping head around its longitudinal clamping head axisto a rotation of the bone screw around its longitudinal screw axis whilean angle between the longitudinal clamping head axis and thelongitudinal screw axis is non-zero, a stabilization bar supportconfigured to receive a stabilization bar and permit said transmissionwhile the bar is attached to the implant; and an elongated stabilizationbar having a first distal end and a second distal end, the barcomprising a pair of generally parallel rods having a space between therods, with the space having an opening along at least one of the distalends of the bar, and with the space being sufficient sized to allowpassage of the clamping head along a path from the opening to a pointbetween the distal ends.
 18. The system of claim 17, in which thestabilization bar support is configured to allow the rods to slidelaterally across the stabilization bar support as the clamping head ispassed along a path from the opening to a point between the distal ends.19. The system of claim 18, in which stabilization bar support isrotatable about the clamping head with the clamping head disposedbetween the rods of the bar.
 20. The system of claim 19, in which one ofthe implants has a housing in an end of the bone screw in which an endof the clamping head is disposable, and that end of the clamping headhas a projection configured to cooperate with a concave portion of thehousing to prevent rotation, relative to the bone screw, of the clampinghead around the longitudinal clamping head axis.